A penguin waddles along the central axis of a concave mirror, from the focal poi

Question

A penguin waddles along the central axis of a concave mirror, from the focal point to an effectively infinite distance. Which of these statements are true? (Select all that apply.)

a.The penguin's image moves from infinity to the focal point.
b.The penguin's image moves from the focal point to infinity.
c.The penguin's image moves in a more complicated manner.
d.The height of the image increases continuously.
e.The height of the image decreases continuously.
f.The height of the image changes in a more complicated manner.

Explanation / Answer

   1/f   =   1/v   +   1/u    f   =   focal length of mirror    u   =   object distance    Initially,   u   =   f    =>   image distance   vinitial   =   f * f / (f - f)                                              =   f2 / 0                                              =   8    Finally   u   =   8            1/vfinal   =   1/f   -   1/8                vfinal      =   f          hence the image will waddle between infinity and focus.    magnification   m   =   - v / u    minitial   =  - 8 / f                   =  - 8    and   mfinal   =   - f / 8                      =   0    i.e. the image will vary from very very large to very very small.    Hence correct choices are    a.The penguin's image moves from infinity to the focal point.    e.The height of the image decreases continuously.

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